Tonight my aunt and I went to dinner again.
I tried dealing with the bill by paying it in full with the tip when she went to the restroom just before we left. I thought we were fine until we got to my car (I do the driving on these occasions). She asked me how much she owed me. I replied, "Zero." She said, "No, no, no, no, no!" We were on our way back to her house, so I said, "Why don't we settle up at your house?"
I was hoping she'd forget about it, but when we got there, she asked me again how much she owed me. The cost of the whole meal for both of us, plus the tip, was $40, so I decided going halves would be fair and told her $20. She gave me a $20 bill and I put it on the coffee table in her living room (I was still hoping she'd forget it). We sat and chatted for a while, and then I got up to go. She noticed that the $20 bill was on the coffee table and pointed it out, so I picked it up and took it with me.
I guess I made some progress if she agreed to halves, even if she did force that on me.